Field of the Invention:
The invention relates to a clutch system with a clutch device, an actuating device for the hydraulic actuation of the clutch device, and a hydraulic system. The hydraulic system has a master cylinder which can be actuated by way of the actuating device, a slave cylinder, which is connected to the master cylinder by way of a pressure line, for actuating the clutch device, a (first) branch line which is connected to the pressure space of the master cylinder or is disposed between the pressure spaces of the master cylinder and slave cylinder, and a compensating tank volume to which the first branch line is connected.
Use is made largely of hydraulic releasing systems for actuating the clutch in vehicles with shift transmissions, in particular manual shift transmissions. The systems are composed in particular of the pedal arrangement, the master cylinder, the line and the slave cylinder with releasing or a central releaser. The master cylinder is actuated by the driver via the clutch pedal and the slave cylinder actuates the clutch via the release lever and the release bearing or the central releaser directly actuates the clutch. The clutch hydraulics are connected via the master cylinder to a compensating tank.
On account of different phenomena, air inclusions can occur in the clutch hydraulics. In the majority of motor vehicles, sufficient self-ventilating is possible via the master cylinder and compensating tank by means of a rising pressure line from the slave cylinder to the master cylinder.
If self-ventilating of the clutch hydraulics via the master cylinder is hindered by a long pressure line, line sections with a small gradient and/or siphons, this can lead to an accumulation of the air inclusions and therefore to a displacement of the release force characteristic curve of the clutch. The displacement causes inter alia a change in the resulting pedal restoring force and a reduction of the free movement of the clutch. The correct functioning of the clutch system, in particular of the pedal arrangement, release system and clutch, is therefore no longer ensured.
A clutch system of the generic type specified in the above text is known from practice.
European patent EP 1 356 212 B1 and its counterpart U.S. Pat. No. 6,889,811 B2 describe an hydraulically actuable clutch system which is provided with a ventilation device for the hydraulic system. In that clutch system, two valves—a supply valve and a discharge valve—are opened together for the ventilation of the hydraulic slave cylinder, such that flow passes through the hydraulic system for a certain period of time and the resulting oil flow ventilates the slave cylinder.
German published patent application DE 101 01 438 A1 discloses a ventilation device for a hydraulic system in a clutch system. That ventilation device is characterized by an automatic mode of operation. There, the ventilation takes place if a pressure is built up in the initially unpressurized hydraulic system. For this purpose, a ventilation valve is arranged at the highest point of a line of a slave cylinder. An electromagnetic control valve is situated between the ventilation valve and a pressure accumulator, with the ventilation valve being connected via a recirculation line to a compensating tank. The ventilation valve comprises a valve housing, a valve body and a preload spring. The mode of operation of the ventilation valve assumes that the system to be ventilated is at least briefly unpressurized. In the unpressurized state, the valve body of the ventilation valve is pressed under the force of the preload spring against a lower sealing surface of the valve housing, and thereby prevents the infiltration of air from the recirculation line. If the control valve is opened, the valve body rises up from the lower sealing face and air present in the recirculation line can escape.